The invention relates to a method for identifying the position of a rotor of an electric motor, in which a target arranged on a rotor is scanned with a sensor, as well as a target for determining a position of a rotor of an electric motor, and an electric motor.
In modern motor vehicles, particularly in passenger vehicles, increasingly automatic clutches are used, as described for example in DE 10 2011 014 936 A1, Here the clutch is moved by an electrically commutated motor. In order to determine the precise position of the clutch it is necessary to precisely determine the position of the electric motor within one rotation of the motor using a sensor for the position of a rotor.
From DE 10 2013 208 986 A1 a magnetic master ring of a sensor is known for the position of a rotor for an electrically commutated electric motor, which shows a predetermined number of magnetic poles with an alternating direction of magnetization. Such a magnetic master rings is scanned with a sensor system, which is based on the physical principles of the Hall effect, the AMR, or the GMR-measurement. The target embodied as a permanent magnet leads to high costs for the magnetic raw material, though, and is not easily integrated in the rotor system, because the magnetic material is very brittle and expansion coefficients are given here, which are dependent on the direction and are very different for synthetic materials and metals.
In such sensor systems for the position of a rotor any change of the distance between the target and the sensor, for example caused by the swiveling rotor shafts or any flaws of the magnetization, severely influence the measuring signal.
A method for the inductive generation of an electric measuring signals is known from WO 2010/084000 A1 depending on a parameter to be measured, such as for determining the path and/or the position in space and/or material features of a test body to be detected.